PMID: 2124140Dec 6, 1990Paper

Selective uptake of 2-thiouracil into melanin-producing systems depends on chemical binding to enzymically generated dopaquinone

Biochimica Et Biophysica Acta
A PalumboG Prota

Abstract

2-Thiouracil (TU), an antithyroid drug, is receiving growing interest as a specific tumor marker for malignant melanoma, owing to its capability of being selectively accumulated into active melanin-producing tissues. However, up until now, the molecular mechanism of TU uptake by growing melanin has remained largely unknown. In an attempt to fill this gap, we have investigated the effect of TU on the tyrosinase catalyzed oxidation of tyrosine. At a concentration of 0.5 mM, TU was found to totally inhibit melanin formation by tyrosinase catalyzed oxidation of 0.25 mM tyrosine in phosphate buffer at pH 6.8. Polarographical monitoring of oxygen consumption under conditions of complete suppression of melanogenesis revealed a significant tyrosinase activity, with TU acting as a modest non-competitive inhibitor of the enzyme (Ki = 0.6 mM). HPLC and TLC analysis of the tyrosine-tyrosinase reaction in the presence of excess TU showed that the substrate is progressively consumed and a major hitherto unknown product (lambda max = 284 nm), positive to ninhydrin and ferric chloride, is concomitantly formed. This was isolated by repeated gel filtration chromatography of the reaction mixture on Sephadex G-10 and was formulated as the TU-dopa ...Continue Reading

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Jan 11, 2001·Nuclear Medicine and Biology·U MårsA Sundin
Jun 1, 1993·Pigment Cell Research·B S Larsson
Aug 1, 1993·Pigment Cell Research·P A Riley
Aug 1, 1995·Pigment Cell Research·U Mårs, B S Larsson
Sep 3, 2003·Pigment Cell Research·Patrick A Riley
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Jul 13, 2006·The Journal of Physical Chemistry. a·Artem KhvorostovMaciej J Nowak
Feb 19, 2002·Chemical Reviews·Albert H. SolowayJ. Gerald Wilson

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